1. Field of the Invention
This invention relates to new white high and low refractive index pigments and aims generally to improve the same and provide novel processes for the production thereof.
2. Description of the Prior Art
In the prior art the so-called white high and low refractive index inorganic pigments, including many of the so-called "Filler" or "Extender" pigments have been subjected to many physical and chemical treatments to render them more attractive to the user both as regards their physical characteristics and also their chemical behavior when incorporated into the system of ultimate usage.
Numerous chemical treatments to modify the surface of such pigments have been tried in order to improve the working and dispersibility characteristics of such inorganic pigments.
Since one of the major uses for such pigmentary material is in the field of modifying or extending colored pigments both organic and inorganic, the fact that the white inorganic pigments are generally inert and difficult to combine with colored pigments or indeed with any vehicle of use without considerable and expensive physical mixing and grinding, the modification of said inorganic pigments to improve such characteristics has been the subject of long and intensive effort on the part of the producers of same. In particular the prevention of reagglomeration of such pigmentary material into hard agglomerates of an average size larger than the normal pigmentary size range of 0.2 to 0.4 micron has never been satisfactorily solved. Many processes and procedures have been attempted, including extensive mechanical working and various surface treatments with oleophilic substances including polymeric compounds but those procedures have involved relative high cost of such treatment, excessive in comparison to the advantages obtained and the low cost of this class of inorganic pigment material as a whole, and such treatments have failed to provide improvement except in certain specific cases within narrow limits of utility. Extensive grinding of inorganic pigments can destroy their utility, inasmuch as their "hiding power" is sharply reduced below certain well defined limits (0.2 micron), and dry grinding thereof is expensive and time consuming as well as presenting a health hazard in the production of considerable quantities of air contaminating dust.